Wide-angle imaging optical system and wide-angle imaging apparatus surveillance imaging apparatus vehicle-mounted imaging apparatus and projection apparatus using the wide-angle imaging optical system

ABSTRACT

A wide-angle imaging optical system includes a refractive optical system ( 3 ), a reflective optical system, and an image-forming optical system ( 5 ). The reflective optical system includes a first reflection surface ( 1 ) that directly reflects rays of light from an object, and a second reflection surface ( 2 ) that reflects rays of light from the first reflection surface ( 1 ). An open portion is provided between the first reflection surface ( 1 ) and the second reflection surface ( 2 ), and rays of light from the object enter the open portion. A light-transmitting portion ( 2   a ) is provided in the second reflection surface ( 2 ) and transmits rays of light that have entered the refractive optical system ( 3 ). An aperture ( 1   a ) is provided in the first reflection surface ( 1 ) and allows rays of light from the second reflection surface ( 2 ) and the refractive optical system ( 3 ) to enter the image-forming optical system ( 5 ).

TECHNICAL FIELD

The present invention relates to a wide-angle imaging apparatus that canproduce a panoramic image covering an ultra-wide range by using thecombination of reflection surfaces and the combination of lenses.

BACKGROUND ART

Various research and development have been conducted on a wide-angleimaging apparatus to efficiently produce an image of an object in alarge area. One example is the development of a wide-angle camera with afish-eye lens.

JP 10(1998)-54939 A (REFLECTION TYPE VIEWING ANGLE CONVERTING OPTICALDEVICE AND OPTICAL SYSTEM USING THE DEVICE) proposes a system thatproduces an image of a wide visual field by variously changing theshapes of three mirror surfaces arranged opposite to each other. JP2000-4383 A (MULTIDIRECTIONAL IMAGE TAKING-IN DEVICE) proposes anoptical system that produces a counter image inside a normal image byusing a shaft of a panoramic image block as a lens.

JP 2001-94839 A (WIDE VISUAL FIELD IMAGE PICKUP DEVICE AND WIDE VISUALFIELD IMAGE PICKUP DISPLAY DEVICE) proposes a device that includes aconvex main mirror having a hole in the center, a convex sub-mirrorhaving a hole in the center, and a lens arranged in the hole of thesub-mirror. Rays of light are reflected by the main mirror, furtherreflected by the sub-mirror, and then are imaged. This image and animage formed by the lens are displayed on the device. WO00/41024(PANORAMIC IMAGING APPARATUS) proposes a system that provides asubstantially flat and stigmatic image plane by using two reflectorssuch as a convex hyperboloidal mirror and a concave ellipsoidal orspherical mirror, a relay system, and an image sensor.

In recent years, an electrical light receiving element, e.g., asolid-state imaging device has been used often. In this case, opticalmembers such as an optical low-pass filter and a near-infrared cutofffilter are arranged between an imaging lens and the imaging device, andthus a relatively long back focal length is necessary. The opticallow-pass filter removes moiré by attenuating a high frequency componentnot less than a spacial frequency component required for takingpictures. The near-infrared cutoff filter corrects a spectral responseof an electrical photoreceptor.

However, a wide-angle imaging optical system using, e.g., a fish-eyelens generally requires many lenses. Therefore, the weight of theoptical system is increased, and the apparatus becomes large andexpensive. Moreover, the generation of chromatic aberration or the likeis a problem, and actually this wide-angle imaging optical system isonly used for taking pictures with special techniques.

JP 10(1998)-54939 A discloses the formation of an image in the vicinityof the axial direction, while a means for correcting various aberrationsis limited. For a multidirectional image capture device of JP 2000-4383A, incident light from the object side passes through a peripherallight-transmitting plane and a rotating body before reaching aperipheral light-proof plane. Therefore, a transparent material used forthe rotating body is thick, and when the transparent material is resin,it is susceptible to temperature changes and takes longer to be molded.When the transparent material is glass, particularly aspherical glass,considerable cost is involved in polishing the glass.

An image pickup device of JP 2001-94839 A can produce two imagessimultaneously: an image formed in such a manner that rays of light arereflected by the main mirror, further reflected by the sub-mirror, andthen are imaged; and an image formed by the lens that is arranged in thesub-mirror. The optical system includes the convex main mirror, theconvex sub-mirror, and the concave lens. Moreover, a master lens shouldbe placed between an imaging device and the sub-mirror. In this case,the F number of the master lens is high, and rays of light entering themaster lens are divergent light due to the configuration of the opticalsystem. Consequently, the master lens becomes large and complicated.

A panoramic imaging apparatus of WO00/41024 requires a relay opticalsystem to form an intermediate image in the optical system, and thus theentire length of the optical system is increased, resulting in a largerapparatus.

As described above, when an electrical light receiving element is used,it is necessary not only to ensure a relatively long back focal lengthso that optical members such as an optical low-pass filter and anear-infrared cutoff filter are provided, but also to correct aberrationsufficiently. To achieve this, however, relatively many lenses arerequired, and an optical design to reduce the number of lenses should beaddressed.

DISCLOSURE OF INVENTION

To solve the above conventional problems, it is an object of the presentinvention to provide a wide-angle imaging optical system that canproduce a panoramic image covering a maximum horizontal angle of view of360 degrees as well as an image in the vicinity of the axial directionwith a simple structure and has a relatively long back focal length,improved aberration correction, and brightness.

A wide-angle imaging optical system of the present invention includes arefractive optical system, a reflective optical system, and animage-forming optical system. The reflective optical system and theimage-forming optical system are arranged in the indicated order as seenfrom a longer conjugate distance side and constitute a first opticalsystem. The refractive optical system and the image-forming opticalsystem are arranged in the indicated order as seen from the longerconjugate distance side and constitute a second optical system. Thereflective optical system includes a first reflection surface thatdirectly reflects rays of light from an object, and a second reflectionsurface that reflects rays of light from the first reflection surface.An open portion is provided between the first reflection surface and thesecond reflection surface, and rays of light from the object enter theopen portion. Alight-transmitting portion is provided in the secondreflection surface and transmits rays of light that have entered therefractive optical system. An aperture is provided in the firstreflection surface and allows rays of light from the second reflectionsurface and the refractive optical system to enter the image-formingoptical system.

A wide-angle imaging apparatus of the present invention includes thewide-angle imaging optical system of the present invention and animaging device for picking up an image formed by the image-formingoptical system.

A surveillance imaging apparatus of the present invention includes thewide-angle imaging optical system of the present invention.

A vehicle-mounted imaging apparatus of the present invention includesthe wide-angle imaging optical system of the present invention.

A projection apparatus of the present invention includes the wide-angleimaging optical system of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 1 of the present invention.

FIG. 2 is a schematic side view of a wide-angle imaging apparatusaccording to Embodiment 1 of the present invention.

FIG. 3 is a view in the direction of the arrow A in FIG. 2.

FIG. 4 is a schematic perspective view of a wide-angle imaging apparatusaccording to Embodiment 1 of the present invention.

FIG. 5 is a schematic view of an image that appears on an imaging deviceof a wide-angle imaging apparatus according to Embodiment 1 of thepresent invention.

FIG. 6 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 2 of the present invention.

FIG. 7 is a schematic cross-sectional view of another example of awide-angle imaging apparatus according to Embodiment 2 of the presentinvention.

FIG. 8 is a schematic cross-sectional view of yet another example of awide-angle imaging apparatus according to Embodiment 2 of the presentinvention.

FIG. 9 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 3 of the present invention.

FIG. 10 is a schematic cross-sectional view of another example of awide-angle imaging apparatus according to Embodiment 3 of the presentinvention.

FIG. 11 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 4 of the present invention.

FIG. 12 is a schematic cross-sectional view of another example of awide-angle imaging apparatus according to Embodiment 4 of the presentinvention.

FIG. 13 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 5 of the present invention.

FIG. 14 is a schematic view of an image that appears on an imagingdevice of a wide-angle imaging apparatus according to Embodiment 5 ofthe present invention.

FIG. 15 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 6 of the present invention.

FIG. 16 is a schematic cross-sectional view of another example of awide-angle imaging apparatus according to Embodiment 6 of the presentinvention.

FIG. 17 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 7 of the present invention.

FIG. 18 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 8 of the present invention.

FIG. 19 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 9 of the present invention.

FIG. 20 is a schematic view of an image that appears on an imagingdevice of a wide-angle imaging apparatus according to Embodiment 9 ofthe present invention.

FIG. 21 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 10 of the present invention.

FIG. 22 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 11 of the present invention.

FIG. 23 is a schematic perspective view showing a wide-angle imagingapparatus according to Embodiment 12 of the present invention.

FIG. 24 is a schematic perspective view of another example of awide-angle imaging apparatus according to Embodiment 12 of the presentinvention.

FIG. 25 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 13 of the present invention.

FIG. 26 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 14 of the present invention.

FIG. 27 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 15 of the present invention.

FIG. 28 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 16 of the present invention.

FIG. 29 is a schematic cross-sectional view of a wide-angle imagingapparatus according to Embodiment 17 of the present invention.

FIG. 30 is a schematic view of an image that appears on an imagingdevice of a wide-angle imaging apparatus according to Embodiment 17 ofthe present invention.

FIG. 31 is a schematic cross-sectional view of another example of awide-angle imaging apparatus according to Embodiment 17 of the presentinvention.

FIG. 32 is a schematic view of an image that is formed by changing themagnification and appears on an imaging device of another example of awide-angle imaging apparatus according to Embodiment 17 of the presentinvention.

FIG. 33 is a schematic perspective view of a wide-angle imagingapparatus according to Embodiment 18 of the present invention.

FIG. 34 is a schematic perspective view of another example of awide-angle imaging apparatus according to Embodiment 18 of the presentinvention.

FIG. 35 is a schematic perspective view of yet another example of awide-angle imaging apparatus according to Embodiment 18 of the presentinvention.

FIG. 36A shows the spherical aberration of a first optical system inExample 1 of the present invention.

FIG. 36B shows the astigmatism of a first optical system in Example 1 ofthe present invention.

FIG. 36C shows the distortion of a first optical system in Example 1 ofthe present invention.

FIG. 37A shows the spherical aberration of a second optical system inExample 1 of the present invention.

FIG. 37B shows the astigmatism of a second optical system in Example 1of the present invention.

FIG. 37C shows the distortion of a second optical system in Example 1 ofthe present invention.

FIG. 38A shows the spherical aberration of a first optical system inExample 2 of the present invention.

FIG. 38B shows the astigmatism of a first optical system in Example 2 ofthe present invention.

FIG. 38C shows the distortion of a first optical system in Example 2 ofthe present invention.

FIG. 39A shows the spherical aberration of a second optical system inExample 2 of the present invention.

FIG. 39B shows the astigmatism of a second optical system in Example 2of the present invention.

FIG. 39C shows the distortion of a second optical system in Example 2 ofthe present invention.

FIG. 40 is a schematic cross-sectional view showing an example of thecombination of reflection surfaces according to Embodiment 19 of thepresent invention.

FIG. 41 is a schematic perspective view of a wide-angle imagingapparatus according to claim 20 of the present invention.

FIG. 42 shows a light transmission curve of Si₂AsTe₂.

FIG. 43 is a schematic view of an embodiment of a surveillancewide-angle imaging apparatus of the present invention.

FIG. 44 is a schematic view of an embodiment of a vehicle-mountedwide-angle imaging apparatus of the present invention.

FIG. 45 is a schematic view of an embodiment of a projection wide-angleimaging apparatus of the present invention.

FIG. 46 is a schematic view of a vehicle-mounted imaging apparatusaccording to Embodiment 25 of the present invention.

FIG. 47 is a schematic view of a vehicle-mounted imaging apparatusaccording to Embodiment 25 of the present invention when a mountingangle is changed.

FIG. 48 is a schematic view of a vehicle-mounted imaging apparatusaccording to Embodiment 26 of the present invention.

FIG. 49 shows a wide-area image of a vehicle-mounted imaging apparatusaccording to Embodiment 26 of the present invention.

FIG. 50 shows a wide-area image of a vehicle-mounted imaging apparatusaccording to Embodiment 26 of the present invention when a vehicle in animaging area moves.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention includes the reflective optical system with thefirst reflection surface and the second reflection surface, the openportion provided between the first reflection surface and the secondreflection surface, the light-transmitting portion provided in thesecond reflection surface, and the aperture provided in the firstreflection surface, thereby producing a panoramic image that covers awide range, i.e., a maximum horizontal angle of view of 360 degrees anda vertical angle of view of about 180 degrees. Moreover, the mainoptical system can be composed of reflection surfaces that cause nochromatic aberration. This reduces not only man-hours for design butalso constraints on fabrication, so that a small, lightweight, low-cost,and bright wide-angle imaging optical system can be achieved.

In the present invention, it is preferable that the first optical systemand the second optical system share the image-forming optical system.This configuration can reduce the size of the apparatus.

It is preferable that no intermediate image is formed inside thewide-angle imaging optical system. With this configuration, thewide-angle imaging optical system is not a relay optical system, and theentire length of the optical system is reduced, so that a smallerapparatus can be achieved.

The wide-angle imaging optical system preferably satisfies therelationship expressed byfa>0fb>0where fa is a combined focal length of the first optical system, and fbis a combined focal length of the second optical system. With thisconfiguration, the wide-angle imaging optical system is not a relayoptical system, and the entire length of the optical system is reduced,so that a smaller apparatus can be achieved. When fa is not more thanthe lower limit, an intermediate image is formed inside the firstoptical system, and thus the image of an object formed by the firstoptical system is an erect image. Moreover, the first optical systembecomes a relay optical system, which increases the entire length of theoptical system.

When fb is not more than the lower limit, an intermediate image isformed inside the second optical system, and thus the image of an objectformed by the second optical system is an erect image. Moreover, thesecond optical system becomes a relay optical system, which increasesthe entire length of the optical system. In this case, when the imageformed by the first optical system is inverted, the resultant image isnot continuous.

The wide-angle imaging optical system preferably satisfies therelationship expressed byf2≧dwhere f2 is a focal length of the second reflection surface, and d is adistance on the axis between the first reflection surface and the secondreflection surface. This configuration easily can correct aberration inthe image-forming optical system. When f2≧d is not satisfied, anintermediate image is formed inside the reflective optical system, andthe angle of deviation of rays of light passing through theimage-forming optical system becomes larger, thus making it difficult tocorrect aberration in the image-forming optical system. Moreover, theimage formed by the first optical system is an erect image. Therefore,when the image formed by the second optical system is inverted, theresultant image is not continuous.

The wide-angle imaging optical system preferably satisfies therelationship expressed by|f12/fa|>5where fa is a combined focal length of the first optical system, and f12is a combined focal length of the first reflection surface and thesecond reflection surface. This configuration can reduce the entirelength of the optical system. |f12/fa| represents the degree of a focalsystem of the reflection surfaces. When the value is not more than thelower limit, the combined focal length of the first and secondreflection surfaces is reduced. Therefore, a relay optical system ratherthan an a focal system is provided while an intermediate image is formedinside the wide-angle imaging optical system, so that the entire lengthof the optical system becomes longer.

The wide-angle imaging optical system preferably satisfies therelationship expressed byr2>00.3<r1/r2<0.7where r1 is a radius of curvature of the first reflection surface, andr2 is a radius of curvature of the second reflection surface. Thisconfiguration can achieve a small bright optical system. When r2 is notmore than the lower limit, the second reflection surface has a convexsurface as seen from incident light from an object, and rays of lightentering the image-forming optical system are divergent light.Therefore, the image-forming optical system itself becomes larger, whichin turn increases the size of the apparatus.

When the value is not less than the upper limit of 0.3<r1/r2<0.7, raysof light from the second reflection surface enter the aperture at alarger angle, thus making it difficult to correct aberration in theimage-forming optical system. Moreover, the aperture efficiency also isreduced, so that brightness cannot be ensured at the periphery. When thevalue is not more than the lower limit, the area used by the firstoptical system on the second reflection surface extends to near thecentral axis, and thus the area of the light-transmitting portionbecomes narrower. Consequently, rays of light from the secondimage-forming optical system do not pass through the light-transmittingportion, and an image cannot be formed.

The wide-angle imaging optical system preferably satisfies therelationship expressed by|fb−fa|/|fa|<0.5where fa is a combined focal length of the first optical system, and fbis a combined focal length of the second optical system. Thisconfiguration can prevent missing or overlapping of images. When thevalue is not less than the upper limit of |fb−fa|/|fa|<0.5, a differencein back focal length between the first optical system and the secondoptical system is increased. Moreover, since the magnification for imageformation of the first optical system differs from that of the secondoptical system, an annular image formed by the first optical system anda circular image formed by the second optical system are not continuous,resulting in missing or overlapping of images.

The wide-angle imaging optical system preferably satisfies therelationship expressed by1.2<bf/fi<1.8where bf is a back focal length of the image-forming optical systemmeasured in terms of air when rays of light from an object at infinityenter the image-forming optical system in parallel, and fi is a combinedfocal length of the image-forming optical system. This configuration canreduce the entire length of the optical system. When the value is notless than the upper limit of 1.2<bf/fi<1.8, the back focal length isincreased to make the entire length of the optical system longer, whichin turn increases the size of the apparatus. When the value is not morethan the lower limit, the back focal length is reduced, and the opticalsystem cannot be provided.

It is preferable that the refractive optical system includes a firstlens group with negative power and a second lens group with positivepower that are arranged in the indicated order as seen from the objectside. With this configuration, the wide-angle imaging optical systemdoes not form any intermediate image at a halfway point, and a brightoptical system can be achieved.

It is preferable that at least one of the first reflection surface andthe second reflection surface is a rotationally symmetrical asphericsurface in shape. This configuration optimally can correct curvature offield or astigmatism generated in the reflective optical system itselfby using an aspherical coefficient.

It is preferable that a magnification for image formation of the firstoptical system and a magnification for image formation of the secondoptical system have the same sign. With this configuration, when theimage formed by the first optical system is an erect image, the imageformed by the second optical system also is an erect image. Moreover,when the image formed by the first optical system is an inverted image,the image formed by the second optical system also is an inverted image.Therefore, a continuous image can be obtained.

It is preferable that a magnification for image formation of the firstoptical system and a magnification for image formation of the secondoptical system are both negative. With this configuration, thewide-angle imaging optical system is not a relay optical system, and theentire length of the optical system is reduced, so that a smallerapparatus can be achieved.

It is preferable that at least one focal point of the first reflectionsurface coincides with at least one focal point of the second reflectionsurface. A rotationally symmetrical aspheric surface has one or twofocal points. This configuration allows a chief ray to converge on theposition of the focal point by combining the first reflection surfacewith the second reflection surface.

It is preferable that a lens stop is located inside the image-formingoptical system or between the image-forming optical system and thesecond reflection surface. With this configuration, one of the focalpoints of the second reflection surface coincides with the center of thelens stop. Therefore, rays of light can be imaged by the image-formingoptical system while a chief ray converges on the position of the lensstop.

It is preferable that a focal point of the second reflection surfacecoincides with the center of the lens stop.

It is preferable that a shielding member is formed near the periphery ofthe aperture. This configuration can eliminate ghost light that isreflected four or more times by the reflection surfaces, enters theaperture, and is picked up after passing through the image-formingoptical system.

It is preferable that the shielding member supports the image-formingoptical system. This configuration can use the shielding memberefficiently without relying on a special member for supporting theimage-forming optical system.

It is preferable that the image-forming optical system includes a hoodthat limits rays of light entering the image-forming optical system.This configuration can prevent a circular image of a second imaging area(where rays of light enter the refractive optical system) fromoverlapping with an annular image of a first imaging area (where rays oflight enter the reflective optical system) that is formed outside thecircular image when they are picked up by the imaging device.

It is preferable that the lenses of the image-forming optical system arearranged in the following order as seen from the object side: a negativelens, a positive lens, and a positive lens. This configuration allowsthe image-forming optical system to have a relatively long back focallength, improved aberration performance, and brightness even with asmall number of lenses.

It is preferable that the lenses of the image-forming optical system arearranged in the following order as seen from the object side: a negativelens, a positive lens, a positive lens, and a positive lens. Thisconfiguration allows the image-forming optical system to have arelatively long back focal length, improved aberration performance, andbrightness even with a small number of lenses.

It is preferable that the refractive optical system includes a hood thatlimits rays of light entering the refractive optical system. Thisconfiguration can prevent a circular image of a second imaging area(where rays of light enter the refractive optical system) fromoverlapping with an annular image of a first imaging area (where rays oflight enter the reflective optical system) that is formed outside thecircular image when they are picked up by the imaging device.

It is preferable that the first reflection surface is formed integrallywith a lens of the image-forming optical system. This configuration canimprove the manufacturing cost and efficiency and reduce the number ofoptical components required for the wide-angle imaging optical system.Moreover, the deviation between the optical axes of optical elements inthe reflective optical system and the image-forming optical system isreduced, thereby making the optical system resistant to vibration. Thus,the optical system can maintain high performance, particularly when usedas a vehicle-mounted optical system.

It is preferable that the shape of the first reflection surface issubstantially the same as the shape of a portion of the lens of theimage-forming optical system that corresponds to the aperture.

It is preferable that the shape of the first reflection surface differsfrom the shape of a portion of the lens of the image-forming opticalsystem that corresponds to the aperture. With this configuration, thelens at the aperture can have the same effect as a convex or concavelens, so that various aberrations generated in the wide-angle imagingoptical system can be corrected optimally, thus producing a high-qualityimage that covers a wide range.

It is preferable that the second reflection surface is formed integrallywith a lens of the refractive optical system. This configuration canimprove the manufacturing cost and efficiency and reduce the number ofoptical components required for the wide-angle imaging optical system.Moreover, the deviation between the optical axes of optical elements inthe reflective optical system and the refractive optical system isreduced, thereby making the optical system resistant to vibration. Thus,the optical system can maintain high performance, particularly when usedas a vehicle-mounted optical system. Further, this configurationcombined with the integrally formed first reflection surface and lens ofthe image-forming optical system enables accurate image display andimage processing conversion, since an annular image formed by the firstoptical system and an annular image formed by the second optical systemcan have the same central point more precisely.

It is preferable that the shape of the second reflection surface issubstantially the same as the shape of a portion of the lens of therefractive optical system that corresponds to the light-transmittingportion. This configuration facilitates processing.

It is preferable that the shape of the second reflection surface differsfrom the shape of a portion of the lens of the refractive optical systemthat corresponds to the light-transmitting portion. With thisconfiguration, the lens at the light-transmitting portion can have thesame effect as a convex or concave lens, so that various aberrationsgenerated in the wide-angle imaging optical system can be correctedoptimally, thus producing a high-quality image that covers a wide range.

It is preferable that the image-forming optical system includes a thirdreflection surface that reflects rays of light imaged by theimage-forming optical system. The third reflection surface can reflectrays of light in the direction substantially perpendicular to thecentral axis. Therefore, it is possible to increase the optical pathlength of the wide-angle imaging optical system even in a limited space.

It is preferable that the refractive optical system and theimage-forming optical system are transparent to an infrared wavelengthregion including 1 to 10 μm. With this configuration, the refractiveoptical system and the image-forming optical system transmit light in awide range of wavelength regions from visible to infrared. Thus, theapparatus can be used in a wide range of wavelength regions from visibleto infrared.

A wide-angle imaging apparatus of the present invention includes thewide-angle imaging optical system of the present invention and animaging device for picking up an image formed by the image-formingoptical system. The wide-angle imaging apparatus can produce a panoramicimage that covers a wide range, i.e., a maximum horizontal angle of viewof 360 degrees and a vertical angle of view of about 180 degrees.Moreover, the main optical system can be composed of reflection surfacesthat cause no chromatic aberration. This reduces not only man-hours fordesign but also constraints on fabrication, so that a small,lightweight, low-cost, and bright wide-angle imaging apparatus can beachieved.

In the wide-angle imaging apparatus, it is preferable that a pluralityof wide-angle imaging optical systems and the imaging devices thatcorrespond to each of the plurality of wide-angle imaging opticalsystems are arranged so as to produce separate images of an object. Thisconfiguration not only can produce a panoramic image that covers amaximum horizontal angle of view of 360 degrees, but also can increasethe vertical angle of view compared with the configuration including asingle wide-angle imaging optical system.

It is preferable that two wide-angle imaging optical systems and theimaging devices that correspond to each of the two wide-angle imagingoptical systems are arranged so as to produce separate images of anobject, and when an axis that joins centers of curvature of the firstreflection surface and the second reflection surface is identified as acentral axis, the two wide-angle imaging optical systems are arrangedsymmetrically with respect to an axis perpendicular to the central axis.

It is preferable that the plurality of wide-angle imaging opticalsystems share a single imaging device. This configuration isadvantageous for small size and lightweight.

It is preferable that when an area in which rays of light enter thereflective optical system is identified as a first imaging area, and anarea in which rays of light enter the refractive optical system isidentified as a second imaging area, an image picked up by the imagingdevice includes a circular image that is obtained by taking the secondimaging area and an annular image that is obtained by taking the firstimaging area and formed outside the circular image, and that the firstimaging area and the second imaging area do not overlap with each other,and further that the circular image and the annular image are arrangedcontinuously. This configuration can use the effective area of theimaging device efficiently, eliminate missing or overlapping of images,and ensure accurate imaging.

It is preferable that a protective member is arranged so as to surroundthe open portion. This configuration can protect the reflective opticalsystem easily and effectively.

It is preferable that the protective member is provided with a film forpreventing internal reflection. This configuration effectively caneliminate ghost light that is reflected internally by the protectivemember and travels through the same optical path as normal light whileprotecting the reflection optical system easily and effectively.

It is preferable that the protective member is in the form of asubstantially frustoconical, and the inner diameter of the protectivemember at the first reflection surface differs from the inner diameterof the protective member at the second reflection surface. Thisconfiguration can control the reflection angle of ghost light andprevent the ghost light from traveling through the same optical path asnormal light.

It is preferable that at least one of the refractive optical system andthe image-forming optical system has a zoom function. This configurationcan produce an enlarged image of an object in the vicinity of the axialdirection.

It is preferable that the wide-angle imaging apparatus can be mounted onan object, and a mounting angle can be adjusted. This configurationeasily can change the imaging range.

The wide-angle imaging apparatus preferably includes a moving objectsensing function. With this configuration, a moving object can beextracted, and therefore any motion in the surroundings can be detectedand recognized precisely.

A surveillance imaging apparatus of the present invention includes thewide-angle imaging optical system of the present invention and thus canproduce a panoramic image that covers a wide range of horizontal angleof view as well as vertical angle of view. Moreover, reflection surfacesmade of a material that reflects light in a wide range of wavelengthregions from visible to infrared are combined with lenses made of amaterial that transmits light in the visible to infrared wavelengthregions. Thus, surveillance covering an ultra-wide range can beperformed at any time of day or night.

A vehicle-mounted imaging apparatus of the present invention includesthe wide-angle imaging optical system of the present invention and thuscan produce a panoramic image that covers a wide range of horizontalangle of view as well as vertical angle of view. The image produced isdisplayed on a vehicle-installed monitor, which is installed in thevehicle, so that the vehicle-mounted imaging apparatus can be used,e.g., as a rear view monitor, a front view monitor, or a side viewmonitor.

A projection apparatus of the present invention includes the wide-angleimaging optical system of the present invention and thus can project animage of an object that covers an ultra-wide range by using a projectorsuch as a video projector.

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

Embodiment 1

FIG. 1 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 1, takenalong a plane containing a central axis 9. FIG. 2 is a side view of thesubstantial portion of the apparatus. FIG. 3 is a view in the directionof the arrow A in FIG. 2. FIG. 4 is a perspective view of thesubstantial portion of the apparatus. The wide-angle imaging apparatusin FIG. 1 includes a refractive optical system 3, a reflective opticalsystem composed of a first reflection surface 1 and a second reflectionsurface 2, and an image-forming optical system 5. The central axis 9joins centers of curvature of the first reflection surface 1 and thesecond reflection surface 2.

The optical system of the wide-angle imaging apparatus in FIG. 1includes a first optical system and a second optical system. For thefirst optical system, the reflective optical system and theimage-forming optical system 5 are arranged in the indicated order asseen from a longer conjugate distance side. For the second opticalsystem, the refractive optical system 3 and the image-forming opticalsystem 5 are arranged in the indicated order as seen from the longerconjugate distance side. In the example of FIG. 1, the longer conjugatedistance side is opposite to an image plane (an imaging device 7). Thesame is true in the following drawings.

The first reflection surface 1 has a convex surface as seen fromincident light 8 b (rays of light from a first imaging area) from theoutside (an object). The second reflection surface 2 has a concavesurface as seen from the incident light 8 b. A lens 6 of theimage-forming optical system 5 is formed integrally with the firstreflection surface 1, while a lens 4 of the refractive optical system 3is formed integrally with the second reflection surface 2.

Incident light 8 a (rays of light from a second imaging area) from theoutside (an object) is refracted by the refractive optical system 3,passes through a light-transmitting portion 2 a, i.e., a circularopening provided in the second reflection surface 2 and a circularaperture 1 a provided in the first reflection surface 1, then is imagedby the image-forming optical system 5, and picked up by the imagingdevice 7.

The incident light 8 b is reflected successively by the convex surfaceof the first reflection surface 1 and the concave surface of the secondreflection surface 2, passes through the aperture 1 a provided in thefirst reflection surface 1, then is imaged by the image-forming opticalsystem 5, and picked up by the imaging device 7.

The first reflection surface 1 and the second reflection surface 2 arerotationally aspheric surfaces that are symmetrical with respect to thecentral axis 9. In this embodiment, the first reflection surface 1 andthe second reflection surface 2 are obtained by rotating a parabola.

In FIG. 3, the central axis 9 passes through a point a where centerlines9 a, 9 b cross at right angles. As can be seen from FIGS. 1 to 3, thefirst reflection surface 1 and the second reflection surface 2 arespaced at a predetermined distance away from each other on the centralaxis 9. Thus, an open portion is provided between the first reflectionsurface 1 and the second reflection surface 2 so that the portion isopen toward the whole circumference of a circle whose center is on thecentral axis 9.

Therefore, the incident light 8 a, 8 b from the outside can enter anyposition of an angle θ ranging from 0 to 360 degrees, as shown in FIG.3. In FIG. 1, on the other hand, when a vertical angle of view a isdefined as positive in the counterclockwise direction, the rays of light8 a from the second imaging area are imaged by the wide-angle imagingoptical system at a vertical angle of view a of about −30 to 30 degrees,while the rays of light 8 b from the first imaging area are imaged at avertical angle of view a of about 30 to 90 degrees and −30 to −90degrees. Thus, the wide-angle imaging apparatus of this embodiment has amaximum horizontal angle of view of 360 degrees and a maximum verticalangle of view of about 180 degrees.

FIG. 5 shows the image of an object in a large area that is produced bythe wide-angle imaging apparatus in FIG. 1. A circular image 52 of thesecond imaging area and an annular image 53 of the first imaging areaappear on an imaging device 51. Since the imaging range of the firstimaging area continues to that of the second imaging area, the circularimage 52 and the annular image 53 are formed into a single continuouscircular image. Therefore, the effective area of the imaging device 51can be used efficiently. This image can be produced by making theaperture 1 a and the light-transmitting portion 2 a circular in shape,by adjusting the shape and arrangement of the reflection surfaces in thereflective optical system, and further by adjusting the shape andarrangement of the lenses in the refractive optical system 3 and theimage-forming optical system 5.

It is preferable that a magnification for image formation of the firstoptical system and a magnification for image formation of the secondoptical system have the same sign. Thus, when the image formed by thefirst optical system is an erect image, the image formed by the secondoptical system also is an erect image. Moreover, when the image formedby the first optical system is an inverted image, the image formed bythe second optical system also is an inverted image. Therefore, acontinuous image can be obtained. In this case, it is more preferablethat the magnification for image formation of the first optical systemand the magnification for image formation of the second optical systemare both negative. With the negative sign, the wide-angle imagingoptical system is not a relay optical system, and the entire length ofthe optical system is reduced, so that a smaller apparatus can beachieved. The same is true in the following embodiments.

As described above, this embodiment allows the main optical system to becomposed of reflection surfaces that cause no chromatic aberration.Therefore, not only man-hours for design but also constraints onfabrication can be reduced, providing a small, lightweight, low-cost,and bright wide-angle imaging apparatus. Moreover, the lenses of therefractive optical system and the reflective optical system and thereflection surfaces that are formed integrally with these lenses have anaspheric surface, so that various aberrations generated in the opticalsystem can be corrected. Further, as shown in FIG. 5, it is possible toproduce a panoramic image that covers an ultra-wide range (i.e., amaximum horizontal angle of view of 360 degrees and a maximum verticalangle of view of about 180 degrees) while using the imaging deviceefficiently.

In this embodiment, the first reflection surface 1 and the secondreflection surface 2 are rotationally aspheric surfaces obtained byrotating a parabola. However, the reflection surfaces may be obtained byrotating an ellipse including a circle or a hyperbola. The same is truein the following embodiments.

For each of the lenses 4, 6, the portion provided with the reflectionsurface and the portion corresponding to the light-transmitting portion2 a or the aperture 1 a are formed in a continuous uniform shape.However, the lens shape may be changed, e.g., by reversing the convexityand concavity of the lens at the light-transmitting portion 2 a or theaperture 1 a, which will be described in detail in the followingembodiments.

Embodiment 2

FIGS. 6 and 7 are schematic cross-sectional views showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 2, takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 1 (FIGS. 1 to 5) in basic configuration, but different inthat a third reflection surface 61 with a flat surface of reflection isarranged in the optical path between the image-forming optical system 5and the imaging device 7.

In FIG. 6, incident light 8 a from the outside is refracted by therefractive optical system 3, passes through the light-transmittingportion 2 a provided in the second reflection surface 2 and the aperture1 a provided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by the third reflectionsurface 61 in one direction, and picked up by the imaging device 7.Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes through the aperture 1 aprovided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by the third reflectionsurface 61 in one direction, and picked up by the imaging device 7.Consequently, the optical system can be made shorter in the direction ofthe central axis 9 by using the third reflection surface 61, thusreducing the size of the apparatus.

FIG. 7 is a schematic view showing another example of the basicconfiguration of a wide-angle imaging apparatus in Embodiment 2. Thisconfiguration is different from the configuration in FIG. 6 in that acondenser 5 a is arranged between a third reflection surface 71 with aflat surface of reflection and the imaging device 7 in the image-formingoptical system 5. Like the configuration in FIG. 6, the apparatus can bemade shorter in the direction of the central axis 9 by using the thirdreflection surface 71, thus reducing the size of the apparatus.

For an embodiment as shown in FIG. 8, the basic configuration is thesame as that in FIG. 7, but different in that a third reflection surface81 with a flat surface of reflection is arranged so as to reflect raysof light that have been imaged by the image-forming optical system 5after passing through the aperture 1 a of the first reflection surface 1in the direction substantially perpendicular to the central axis 9. Thismakes it possible not only to reduce the size of the wide-angle imagingapparatus, but also to increase the optical path length of thewide-angle imaging optical system even in a limited space.

Embodiment 3

FIG. 9 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 3, takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 2 (FIGS. 6 to 8) in basic configuration, but different inthat the third reflection surface is curved.

In FIG. 9, incident light 8 a from the outside is refracted by therefractive optical system 3, passes through the light-transmittingportion 2 a provided in the second reflection surface 2 and the aperture1 a provided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by a third reflection surface91 with a curved surface of reflection in one direction, further imagedby the image-forming optical system 5, and picked up by the imagingdevice 7. Incident light 8 b from the outside is reflected successivelyby the convex surface of the first reflection surface 1 and the concavesurface of the second reflection surface 2, passes through the aperture1 a provided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by the third reflectionsurface 91 in one direction, further imaged by the image-forming opticalsystem 5, and picked up by the imaging device 7. The third reflectionsurface 91 is arranged so as to reflect rays of light that have passedthrough the aperture 1 a in the direction substantially perpendicular tothe central axis 9. The third reflection surface 91 may have any curvedsurface such as a cylindrical surface, a toric surface, or a free-formsurface. The free-form surface is a curved surface that does not havethe axis of rotational symmetry.

For an embodiment as shown in FIG. 10, a third reflection surface 101 iscurved and arranged so as to reflect rays of light that have passedthrough the aperture 1 a in the direction substantially perpendicular tothe central axis 9. In this embodiment, the third reflection surface 101has a toric surface or free-form surface, so that the number of lensesin the image-forming optical system is reduced compared with theembodiment in FIG. 9.

Like Embodiment 2, this embodiment can reduce the size of the apparatusby using the third reflection surface. Moreover, the third reflectionsurface is arranged so as to reflect rays of light in the directionsubstantially perpendicular to the central axis 9. Therefore, it ispossible to increase the optical path length of the wide-angle imagingoptical system even in a limited space.

Embodiment 4

FIG. 11 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 4, takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 1 (FIGS. 1 to 5) in basic configuration, but different inthat the shape of each reflection surface differs from the shape of aportion of each lens that corresponds to the aperture and thelight-transmitting portion.

In the configuration in FIG. 1, the shape of the first reflectionsurface 1 is substantially the same as the shape of a portion of thelens 6 that corresponds to the aperture 1 a. Similarly, the shape of thesecond reflection surface 2 is substantially the same as the shape of aportion of the lens 4 that corresponds to the light-transmitting portion2 a.

In the embodiment in FIG. 11, a portion of a lens 111 provided with thefirst reflection surface 1 is formed so that both surfaces, one facingthe object side and the other facing the image plane side, are convextoward the object side. In the aperture 1 a, however, both surfaces areconcave toward the object side. On the other hand, a portion of a lens112 provided with the second reflection surface 2 is formed so that bothsurfaces, one facing the object side and the other facing the imageplane side, are convex toward the object side. In the light-transmittingportion 2 a, however, the surface on the image plane side is concavetoward the object side, while the surface on the object side is convextoward the object side. In this case, the degree of convexity in thelight-transmitting portion 2 a differs from that in the portion of thelens 112 provided with the second reflection surface 2.

Consequently, in the configuration in FIG. 11, the shape of the firstreflection surface 1 differs from the shape of a portion of the lens 111that corresponds to the aperture 1 a. Similarly, the shape of the secondreflection surface 2 differs from the shape of a portion of the lens 112that corresponds to the light-transmitting portion 2 a.

In this configuration, incident light 8 a from the outside is refractedby the refractive optical system 3, passes through thelight-transmitting portion 2 a and the aperture 1 a provided in thefirst reflection surface 1, then is imaged by the image-forming opticalsystem 5, and picked up by the imaging device 7.

Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes through the aperture 1 aprovided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, and picked up by the imaging device 7.As described above, when the basic cross section of the lens in thelight-transmitting portion or aperture is different from the basic crosssection of the lens in a portion provided with the reflection surface,the effect can be comparable to that obtained by arranging a specialconvex or concave lens separately at the light-transmitting portion oraperture. Moreover, various aberrations generated in the wide-angleimaging optical system can be corrected optimally, thus producing ahigh-quality image that covers a wide range.

FIG. 12 is a schematic cross-sectional view showing another example ofthe basic configuration of a wide-angle imaging apparatus in Embodiment4, taken along a plane containing a central axis 9. This embodiment isthe same as Embodiment 1 (FIGS. 1 to 5) in basic configuration, butdifferent in that the first reflection surface 1 and the secondreflection surface 2 are formed integrally with a resin substrate, andspecial lenses different from the resin substrate are arranged at thelight-transmitting portion 2 a and the aperture 1 a, respectively. Inthis embodiment, the shape of the first reflection surface 1 differsfrom the shape of a portion of the lens that corresponds to the aperture1 a. Similarly, the shape of the second reflection surface 2 differsfrom the shape of a portion of the lens that corresponds to thelight-transmitting portion 2 a.

In FIG. 12, the first reflection surface 1 is formed integrally with afirst resin substrate 113, while the second reflection surface 2 isformed integrally with a second resin substrate 114. Incident light 8 afrom the outside is refracted by the refractive optical system 3including a lens 3 a, passes through the light-transmitting portion 2 aprovided in the second reflection surface 2 and the second resinsubstrate 114 and the aperture 1 a provided in the first reflectionsurface 1 and the first resin substrate 113, then is imaged by theimage-forming optical system 5 including a lens 5 b, and picked up bythe imaging device 7.

Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes through the aperture 1 aprovided in the first reflection surface 1 and the first resin substrate113, then is imaged by the image-forming optical system 5, and picked upby the imaging device 7.

As described above, the configuration in FIG. 12 can use special lensesfor the light-transmitting portion 2 a and the aperture 1 a,respectively. Therefore, various aberrations generated in the wide-angleimaging optical system can be corrected optimally by changing the lensarrangement of the refractive optical system 3 and the image-formingoptical system 5, thus producing a high-quality image that covers a widerange.

The image-forming optical system 5 can be held in contact with theaperture 1 a provided in the first reflection surface 1 and the firstresin substrate 113. Alternatively, the image-forming optical system 5also can be held by being inserted into the aperture 1 a. Similarly, therefractive optical system 3 can be held in contact with thelight-transmitting portion 2 a provided in the second reflection surface2 and the second resin substrate 114. Alternatively, the refractiveoptical system 3 also can be held by being inserted into thelight-transmitting portion 2 a. An adhesive or the like may be used tohold the optical systems.

In FIG. 12, only the lens 5 b of the lenses in the image-forming opticalsystem 5 is held by the first resin substrate 113. However, when thelenses are fixed into one component, the entire image-forming opticalsystem 5 can be held by the first resin substrate 113.

In the examples of FIGS. 11 and 12, the reflection surface has adifferent shape from the lens in both of the aperture 1 a and thelight-transmitting portion 2 a. However, the reflection surface may havea different shape from the lens in either of the aperture 1 a or thelight-transmitting portion 2 a.

Embodiment 5

FIG. 13 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 5, takenalong a plane containing a central axis 9. This embodiment uses twowide-angle imaging optical systems of Embodiment 1 as shown in FIG. 1,and they are arranged symmetrically from side to side.

FIGS. 2 to 4 also can be applied to half of the wide-angle imagingoptical systems of this embodiment. Although the illustration thatcorresponds to FIGS. 2 to 4 is not shown in the following embodiments,the illustration of the reflection surfaces is the same as FIGS. 2 to 4.

The basic configuration and operation of half of the wide-angle imagingoptical systems are the same as those in Embodiment 1. Incident light 8a from the outside is refracted by the refractive optical system 3,passes through the light-transmitting portion 2 a provided in the secondreflection surface 2 and the aperture 1 a provided in the firstreflection surface 1, then is imaged by the image-forming optical system5, and picked up by the imaging device 7.

Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes through the aperture 1 aprovided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, and picked up by the imaging device 7.

Like Embodiment 1, half of the wide-angle imaging optical systems has amaximum horizontal angle of view of 360 degrees and a maximum verticalangle of view of 180 degrees. In FIG. 13, a centerline 9 c and thecentral axis 9 cross at right angles, and the two wide-angle imagingoptical systems are symmetrical with respect to the centerline 9 c. Theleft wide-angle imaging optical system has a vertical angle of view ofabout 180 degrees, and the right wide-angle imaging optical system has avertical angle of view of about 180 degrees. In other words, thisembodiment uses two imaging optical systems to produce separate imagesof an object in a large area at a vertical angle of view of 360 degreesin total.

FIG. 14 shows the images of an object in a large area that are producedby the wide-angle imaging apparatus in FIG. 13. A circular image 132 ofthe second imaging area and an annular image 133 of the first imagingarea appear on a first imaging device 131. Since the imaging range ofthe first imaging area continues to that of the second imaging area, thecircular image 132 and the annular image 133 are formed into a singlecontinuous circular image. Therefore, the effective area of the firstimaging device 131 can be used efficiently.

Similarly, a circular image 135 of the second imaging area and anannular image 136 of the first imaging area appear on a second imagingdevice 134. Since the imaging range of the first imaging area continuesto that of the second imaging area, the circular image 135 and theannular image 136 are formed into a single continuous circular image.Therefore, the effective area of the second imaging device 134 can beused efficiently.

As described above, this embodiment can produce a panoramic image thatcovers a maximum horizontal angle of view of 360 degrees. Moreover, thisembodiment can produce an image at a maximum vertical angle of view of360 degrees, compared with about 180 degrees in Embodiment 1.

Embodiment 6

FIGS. 15 and 16 are schematic cross-sectional views showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 6, takenalong a plane containing a central axis 9. This embodiment uses twowide-angle imaging optical systems of Embodiment 2 as shown in FIGS. 6and 7, and they are arranged symmetrically from side to side. The basicconfiguration and operation of half of the wide-angle imaging opticalsystems are the same as those in Embodiment 2.

The configuration in FIG. 15 uses two wide-angle imaging optical systemsas shown in FIG. 6. In FIG. 15, incident light 8 a from the outside isrefracted by the refractive optical system 3, passes through thelight-transmitting portion 2 a provided in the second reflection surface2 and the aperture 1 a provided in the first reflection surface 1, thenis imaged by the image-forming optical system 5, reflected by the thirdreflection surface 61 with a flat surface of reflection in onedirection, and picked up by the imaging device 7.

Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes thought the aperture 1 aprovided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by the third reflectionsurface 61 in one direction, and picked up by the imaging device 7.

The configuration in FIG. 16 uses two wide-angle imaging optical systemsas shown in FIG. 7. In FIG. 16, incident light 8 a from the outside isrefracted by the refractive optical system 3, passes through thelight-transmitting portion 2 a provided in the second reflection surface2 and the aperture 1 a provided in the first reflection surface 1, thenis imaged by the image-forming optical system 5, reflected by the thirdreflection surface 71 with a flat surface of reflection in onedirection, further imaged by the image-forming optical system 5, andpicked up by the imaging device 7.

Incident light 8 b from the outside is reflected successively by theconvex surface of the first reflection surface 1 and the concave surfaceof the second reflection surface 2, passes through the aperture 1 aprovided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, reflected by the third reflectionsurface 71 in one direction, further imaged by the image-forming opticalsystem 5, and picked up by the imaging device 7.

Like Embodiment 2, half of the wide-angle imaging optical systems has amaximum horizontal angle of view of 360 degrees and a maximum verticalangle of view of about 180 degrees. Therefore, this embodiment also canproduce an image at a maximum vertical angle of view of 360 degreesusing two wide-angle imaging optical systems.

Embodiment 7

FIG. 17 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 7, takenalong a plane containing a central axis 9. The basic configuration isthe same as that in Embodiment 6 (FIGS. 15 and 16). This embodiment usestwo wide-angle imaging optical systems as shown in FIG. 9, and isdifferent from Embodiment 6 in that the third reflection surface iscurved. The third reflection surface 91 may have any curved surface suchas a cylindrical surface, a toric surface, or a free-form surface.

As in the case of the third reflection surface with a flat surface, thisembodiment can make the optical system shorter in the direction of thecentral axis 9, thus reducing the size of the apparatus. Moreover, thethird reflection surface is arranged so as to reflect rays of light thathave passed through the aperture 1 a in the direction substantiallyperpendicular to the central axis 9. Therefore, it is possible toincrease the optical path length of the wide-angle imaging opticalsystem even in a limited space.

Embodiment 8

FIG. 18 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 8, takenalong a plane containing a central axis 9. The basic configuration isthe same as that in Embodiment 7 (FIG. 17). This embodiment uses twowide-angle imaging optical systems as shown in FIG. 10, and the thirdreflection surface 101 has a toric surface or free-form surface, so thatthe number of lenses in the image-forming optical system is reduced.With this configuration, the apparatus can be both lightweight andlow-cost.

Embodiments 5 to 8 use two wide-angel imaging optical systems of theembodiments as shown in FIG. 1 or FIGS. 6 to 10. However, the wide-angleoptical systems of the embodiments as shown in FIGS. 11 and 12 also canbe used.

Embodiment 9

FIG. 19 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 9, takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 6 in that two pairs of first and second reflectionsurfaces are arranged symmetrically from side to side, and the thirdreflection surface further is arranged for rays of light that have beenimaged by the image-forming optical system. However, this embodiment isdifferent from Embodiment 6 in that the left optical system and theright optical system share a lens 183 and an imaging device 184 in theimage-forming optical system.

A third reflection surface 181 with a flat surface corresponding to theleft optical system and a third reflection surface 182 with a flatsurface corresponding to the right optical system are arrangedsymmetrically with respect to a centerline 9 d. In each of the right andleft wide-angle imaging optical systems, incident light 8 a from theoutside is refracted by the refractive optical system 3, passes throughthe light-transmitting portion 2 a provided in the second reflectionsurface 2, and enters the aperture 1 a provided in the first reflectionsurface 1. Incident light 8 b from the outside is reflected successivelyby the convex surface the first reflection surface 1 and the concavesurface of the second reflection surface 2, and enters the aperture 1 aprovided in the first reflection surface 1.

The incident light from the left is reflected by the third reflectionsurface 181 in one direction, the incident light from the right isreflected by the third reflection surface 182 in one direction, and thereflected light is imaged by the lens 183 and picked up by the imagingdevice 184.

FIG. 20 shows the image of an object in a large area that is produced bythe wide-angle imaging apparatus in FIG. 19. A circular image 202 of thesecond imaging area and an annular image 203 of the first imaging areathat are formed by the left optical system and a circular image 204 ofthe second imaging area and an annular image 205 of the first imagingarea that are formed by the right optical system appear on an imagingdevice 201.

Since the imaging range of the first imaging area continues to that ofthe second imaging area, the circular image 202 and the annular image203 are formed into a single continuous circular image, and similarlythe circular image 204 and the annular image 205 are formed into asingle continuous circular image. Therefore, the effective area of theimaging device 201 can be used efficiently.

In this embodiment, the right and left optical systems share the lens183 and the imaging device 184, so that the wide-angle imaging apparatuscan be reduced in size, weight and cost.

Embodiment 10

FIG. 21 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 10, takenalong a plane containing a central axis 9. This embodiment is differentfrom Embodiment 9 in that a prism 191 is used instead of the thirdreflection surfaces 181, 182 as shown in FIG. 19.

In this embodiment, the right and left optical systems share the prism191, the lens 183, and the imaging device 184, so that the wide-angleimaging apparatus can be reduced in size, weight and cost further.

The explanation of an image produced by the wide-angle imaging apparatusin this embodiment is the same as that in Embodiment 9 (FIG. 20).

Embodiment 11

FIG. 22 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 11; takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 1 (FIGS. 1 to 5) in basic configuration, but different inthat a cylindrical cover 321 is used as a member for protecting thereflective optical system in the wide-angle imaging optical system. Thecover 321 is made of a resin material having, e.g., a thickness of aboutseveral millimeters.

The cover 321 is arranged so as to surround the open portion between thefirst reflection surface 1 and the second reflection surface 2.Therefore, incident light 8 b from the outside reaches the firstreflection surface 1 through the cover 321. The cover 321 may be usednot only in the wide-angle imaging optical system in FIG. 1, but also inany of the wide-angle imaging optical systems of other embodiments.

In FIG. 22, incident light 8 a from the outside is refracted by therefractive optical system 3, passes through the light-transmittingportion 2 a provided in the second reflection surface 2 and the aperture1 a provided in the first reflection surface 1, then is imaged by theimage-forming optical system 5, and picked up by the imaging device 7.Incident light 8 b from the outside is refracted by the cover 321,reflected successively by the convex surface of the first reflectionsurface 1 and the concave surface of the second reflection surface 2,passes through the aperture 1 a provided in the first reflection surface1, then is imaged by the image-forming optical system 5, and picked upby the imaging device 7. Thus, the cover 321 can protect the reflectiveoptical system easily and effectively.

Embodiment 12

FIGS. 23 and 24 are schematic cross-sectional views showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 12, takenalong a plane containing a central axis 9. The embodiment in FIG. 23 isthe same as that in FIG. 22 in basic configuration, but different inthat an antireflection coating 421 is applied to the inner surface ofthe cover 321. The coating 421 can be formed, e.g., by dipping.

In the configuration in FIG. 23, ghost light 8 c passes through thecover 321 and enters a space in the cover 321. However, the coating 421prevents internal reflection. Therefore, it is also possible to preventthe ghost light 8 c from reaching the imaging device 7 through the sameoptical path as normal light that directly enters the inside of thecover 321, which is indicated by a broken line.

The embodiment in FIG. 24 is the same as that in FIG. 22 in basicconfiguration, but different in that the end of the cover 321 is paintedblack. In the configuration in FIG. 24, ghost light 8 d is cut off atthe end of the cover 321. If the ghost light 8 d is not cut off, itenters the inside of the cover 321, is reflected by the cover 321, andthen reaches the imaging device 7 through the same path as normal lightthat directly enters the inside of the cover 321, which is indicated bya broken line.

Ghost light 8 e entering a space in the cover 321 is cut off at the endof the inner surface of the cover 321. If the ghost light 8 e is not cutoff, it is reflected by this end, further reflected by the firstreflection surface 1, and then reaches the imaging device 7 through thesame path as normal light. Thus, this configuration can prevent both ofthe ghost light 8 d and 8 e from joining halfway through the opticalpath of normal light and reaching the imaging device 7.

In this embodiment, the end of the cover 321 is painted black. However,any shielding member can be provided at the end of the cover 321, e.g.,the end of the cover 321 may be formed of a shielding material.

The basic configuration of the wide-angle imaging optical system is notlimited to the example as shown in FIG. 1, and any of the wide-angleimaging optical systems of other embodiments also can be used.

Embodiment 13

FIG. 25 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 13, takenalong a plane containing a central axis 9. In the configuration in FIG.25, the outer diameter of the second reflection surface 2 is smallerthan that of the first reflection surface 1. A cover 441 is arranged soas to surround the open portion between the first reflection surface 1and the second reflection surface 2. The external shape of the cover 441is a substantially frustoconical, and the inner and outer surfaces aretapered. The cover 441 in the form of a substantially frustoconical ismade of a resin material having, e.g., a thickness of about severalmillimeters.

While Embodiment 12 uses the coating 421 to prevent internal reflectionso that ghost light does not travel through the same optical path asnormal light, this embodiment achieves the same effect with the shape ofthe cover 441. Specifically, as shown in FIG. 25, ghost light 8 centering the inside of the cover 441 is reflected internally by theinclined plane of the cover 441, and the reflected ghost light 8 ctravels through a different optical path from normal light, thuspreventing the generation of ghost light. In other words, thisembodiment can adjust the reflection angle of the ghost light 8 c by theshape of the cover 441, and therefore can prevent the generation ofghost light using the cover 441 itself without coating or the like.

Not only the example as shown in FIG. 25 but also other embodiments mayemploy the above configuration in which the outer diameter of the secondreflection surface is smaller than that of the first reflection surface,and a cover in the form of a substantially frustoconical is used.

Embodiment 14

FIG. 26 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 14, takenalong a plane containing a central axis 9. This embodiment is the sameas that in FIG. 1 in basic configuration, but different in that ashielding member 1 b is formed near the periphery of the aperture 1 a.

Ghost light 8 c is reflected by the reflection surfaces 1 and 2,directed to the reflection surface 1 again, and cut off by the shieldingmember 1 b. When the shielding member 1 b is not used, the ghost light 8c is again reflected by the reflection surfaces 1 and 2 (i.e., the ghostlight 8 c is reflected four times between the reflection surfaces),enters the aperture 1 a, then is imaged by the image-forming opticalsystem 5, and picked up by the imaging device 7, as indicated by abroken line.

In the example as shown in FIG. 26, the ghost light that is reflectedfour times by the reflection surfaces and enters the aperture 1 a is cutoff. However, ghost light to be cut off may be rays of light that arereflected four or more times by the reflection surfaces and enter theaperture 1 a.

The basic configuration of the wide-angle imaging optical system is notlimited to the example as shown in FIG. 1, and any of the wide-angleimaging optical systems of other embodiments also can be used.

Embodiment 15

FIG. 27 is a schematic cross-sectional view showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 15, takenalong a plane containing a central axis 9. This embodiment is the sameas that in FIG. 12 in basic configuration, but different in that a lensbarrel 461 for supporting the image-forming optical system 5 also servesas a shielding member. Therefore, another shielding member is notnecessary, and the lens barrel 461 is used efficiently. In thisconfiguration, ghost light 8 c is reflected by the reflection surfaces 1and 2, and then is cut off by the lens barrel 461. Accordingly, it ispossible to prevent the ghost light from traveling through the sameoptical path as normal light, which is indicated by a broken line.

A hood 462 that is formed, e.g., of a black-painted shielding member,may be provided at the tip of the lens barrel 461. The hood 462 canlimit rays of light entering the image-forming optical system 5 andeliminate unwanted light outside the angle of view that causes straylight or flare.

Reflected light may be generated due to rays of light that enter at anangle approximately equal to the inclination angle of the hood. In sucha case, the hood surface can be made uneven by forming fine steps likestairs, thus allowing the reflected light to diverge.

In this embodiment, the hood is provided in the image-forming opticalsystem 5. However, the refractive optical system including the lens 3 aalso may use a hood to limit rays of light entering the refractiveoptical system.

The basic configuration of the wide-angle imaging optical system is notlimited to the example as shown in FIG. 12, and any of the wide-angleimaging optical systems of other embodiments also can be used.

Embodiment 16

FIG. 28 shows an embodiment of a wide conversion lens that includes awide-angle imaging optical system of the present invention. In the wideconversion lens, an image pickup device 301 for video cameras or camerasis used instead of the image-forming optical system 5 and the imagingdevice 7 of the wide-angle imaging optical system as shown in FIG. 1.This makes it possible to produce an image covering a wide range at atime. Not only the wide-angle imaging optical system in FIG. 1 but alsoany of the wide-angle imaging optical systems of other embodiments canbe used in the wide conversion lens.

Embodiment 17

FIGS. 29 and 31 are schematic cross-sectional views showing the basicconfiguration of a wide-angle imaging apparatus in Embodiment 17, takenalong a plane containing a central axis 9. This embodiment is the sameas Embodiment 1 (FIGS. 1 to 5) in basic configuration, but different inthat the shape of each reflection surface differs from the shape of aportion of each lens that corresponds to the light-transmitting portion2 a and the aperture 1 a, and the refractive optical system and theimage-forming optical system have a zoom function. The explanation ofthe shape of a portion of each lens that corresponds to thelight-transmitting portion 2 a and the aperture 1 a is the same as thatin Embodiment 4.

In FIG. 29, incident light 8 a from the outside is refracted by therefractive optical system 3 including a zoom lens 333, passes throughthe light-transmitting portion 2 a provided in the second reflectionsurface 2 and the aperture 1 a provide in the first reflection surface1, then is imaged by the image-forming optical system 5 including a zoomlens 334, and picked up by the imaging device 7. Incident light 8 b fromthe outside is reflected successively by the convex surface of the firstreflection surface 1 and the concave surface of the second reflectionsurface 2, passes through the aperture 1 a provided in the firstreflection surface 1, then is imaged by the image-forming optical system5 including the zoom lens 334, and picked up by the imaging device 7.

FIG. 30 shows the image of an object in a large area that is produced bythe wide-angle imaging apparatus in FIG. 29. A circular image 341 of thesecond imaging area and an annular image 342 of the first imaging areaappear on the imaging device 7. In FIG. 31, the zoom lens 334 is movedtoward the object side to change the magnification in the wide-angleimaging apparatus in FIG. 29.

FIG. 32 shows the image of an object that is produced by the wide-angleimaging apparatus in FIG. 31. A circular image 361 of the second imagingarea that is obtained by changing the magnification and part of anannular image 362 of the first imaging area that is obtained by changingthe magnification and formed outside the circular image 361 appear onthe imaging device 7. By using the zoom lens, the image of an object inthe vicinity of the central axis is enlarged in the center of theimaging device 7, so that a more detailed image can be produced.

Embodiment 18

FIGS. 33, 34 and 35 are schematic configuration diagrams of a wide-angleimaging apparatus in Embodiment 18. This embodiment is the same asEmbodiment 1 (FIGS. 1 to 5) in basic configuration, but different inlens configuration and the shape of reflection surfaces, which will bedescribed in detail later. In each of FIGS. 33, 34, and 35, numericalsubscript ai (i=1, 2, 3, . . . ) indicates a surface number of the firstoptical system, and bi (i=1, 2, 3, . . . ) indicates a surface number ofthe second optical system. The number of i increases in the order oflight traveling from the object side. The reference numerals rai and rbidenote the radius of curvature of each surface, and dai and dbi denotethe lens thickness or air space that corresponds to each surface.

The shape of the reflection surfaces in this embodiment is arotationally symmetrical aspheric surface including an asphericalcoefficient, and the amount of sag Z is expressed by

$\begin{matrix}{Z = {\frac{h^{2}/R}{1 + \{ {1 - {( {1 + K} )( {h/R} )^{2}}} \}^{1/2}} + {{A2} \times h^{2}} + {{A4} \times h^{4}} + {{A6} \times h^{6}} + {{A8} \times h^{8}} + {{A10} \times h^{10}}}} & {{Formula}\mspace{14mu}(1)}\end{matrix}$where h is a height from the optical axis, R is a radius of curvature ofthe surface, A2 to A10 are aspherical coefficients, and K is a conicalcoefficient.

In this embodiment, the first reflection surface of the reflectiveoptical system has a convex surface, and the second reflection surfacehas a concave surface as seen from incident light from an object.Moreover, the refractive optical system includes a first lens group withnegative power and a second lens group with positive power that arearranged in the indicated order from the object side. Thus, thewide-angle imaging optical system does not form any intermediate imageat a halfway point, and a bright optical system can be achieved.

The position of a lens stop preferably is located inside theimage-forming optical system or between the image-forming optical systemand the second reflection surface. With this configuration, one of thefocal points of the second reflection surface coincides with the centerof the lens stop. Therefore, rays of light can be imaged by theimage-forming optical system while a chief ray converges on the positionof the lens stop. In this embodiment, the position of the lens stop isset to the vertex of the first reflection surface.

The lenses of the image-forming optical system are arranged in thefollowing order as seen from the object side: a negative lens, apositive lens, a positive lens, and a positive lens. Thus, theimage-forming optical system can have a relatively long back focallength, improved aberration correction, and brightness even with a smallnumber of lenses. The lens configuration of the image-forming opticalsystem may be such that a negative lens, a positive lens, and a positivelens are arranged in the indicated order as seen from the object side.

A plate that is inserted between the lens closest to the image side andthe imaging device 7 serves as an optical low-pass filter and anear-infrared cutoff filter. In this embodiment, the shape of the firstreflection surface differs from the shape of a portion of the lens thatcorresponds to the aperture 1 a. Similarly, the shape of the secondreflection surface differs from the shape of a portion of the lens thatcorresponds to the light-transmitting portion 2 a.

In the configurations in FIGS. 33 and 34, the external shape of thesecond reflection surface is smaller than that of the first reflectionsurface, and a tapered conical cover as shown in FIG. 25 is used as amember for supporting and protecting the reflective optical system. Inthe configuration in FIG. 35, the external shape of the first reflectionsurface is substantially the same as that of the second reflectionsurface, and a cylindrical cover as shown in FIG. 22 is used as a memberfor supporting and protecting the reflective optical system.

This embodiment preferably satisfies at least one of the followingformulas (2) to (9):fa>0  Formula (2)fb>0  Formula (3)f2≧d  Formula (4)|f12/fa|>5  Formula (5)r2>0  Formula (6)0.3<r1/r2<0.7  Formula (7)|fb−fa|/|fa|<0.5  Formula (8)1.2<bf/fi<1.8  Formula (9)

In the formula (2), fa is a combined focal length of the first opticalsystem. When fa is not more than the lower limit, an intermediate imageis formed inside the first optical system, and thus the image of anobject formed by the first optical system is an erect image. Moreover,the first optical system becomes a relay optical system, which increasesthe entire length of the optical system.

In the formula (3), fb is a combined focal length of the second opticalsystem. When fb is not more than the lower limit, an intermediate imageis formed inside the second optical system, and thus the image of anobject formed by the second optical system is an erect image. Moreover,the second optical system becomes a relay optical system, whichincreases the entire length of the optical system. In this case, whenthe image formed by the first optical system is inverted, the resultantimage is not continuous.

In the formula (4), f2 is a focal length of the second reflectionsurface, and d is a distance on the axis between the first reflectionsurface and the second reflection surface. When the formula (4) is notsatisfied, an intermediate image is formed inside the reflective opticalsystem, and the angle of deviation of rays of light passing through theimage-forming optical system becomes larger, thus making it difficult tocorrect aberration in the image-forming optical system. Moreover, theimage formed by the first optical system is an erect image. Therefore,when the image formed by the second optical system is inverted, theresultant image is not continuous.

In the formula (5), fa is a combined focal length of the first opticalsystem, and f12 is a combined focal length of the first reflectionsurface and the second reflection surface. The formula (5) representsthe degree of a focal system of the reflection surfaces. When the valueis not more than the lower limit, the combined focal length of the firstand second reflection surfaces is reduced. Therefore, a relay opticalsystem rather than an a focal system is provided while an intermediateimage is formed inside the wide-angle imaging optical system, so thatthe entire length of the optical system becomes longer.

In the formulas (6) and (7), r1 is a radius of curvature of the firstreflection surface, and r2 is a radius of curvature of the secondreflection surface. When r2 is not more than the lower limit in theformula (6), the second reflection surface has a convex surface as seenfrom incident light from an object, and rays of light entering theimage-forming optical system are divergent. Therefore, the image-formingoptical system itself becomes larger, which in turn increases the sizeof the apparatus.

The formula (7) represents a ratio of the radius of curvature of thefirst reflection surface to that of the second reflection surface. Whenthe value is not less than the upper limit in the formula (7), rays oflight from the second reflection surface enter the aperture at a largerangle, thus making it difficult to correct aberration in theimage-forming optical system. Moreover, the aperture efficiency also isreduced, so that brightness cannot be ensured at the periphery. When thevalue is not more than the lower limit in the formula (7), the area usedby the first optical system on the second reflection surface extends tonear the central axis, and thus the area of the light-transmittingportion becomes narrower. Consequently, rays of light from the secondimage-forming optical system do not pass through the light-transmittingportion, and an image cannot be formed.

The formula (8) represents the relationship in combined focal lengthbetween the first optical system and the second optical system anddefines a difference between them. When the value is not less than theupper limit in the formula (8), a difference in back focal lengthbetween the first optical system and the second optical system isincreased. Moreover, since the magnification for image formation of thefirst optical system differs from that of the second optical system, anannular image formed by the first optical system and a circular imageformed by the second optical system are not continuous, resulting inmissing or overlapping of images.

In the formula (9), bf is a back focal length of the image-formingoptical system measured in terms of air when rays of light from anobject at infinity enter the image-forming optical system in parallel,and fi is a combined focal length of the image-forming optical system.When the value is not less than the upper limit in the formula (9), theback focal length is increased to make the entire length of the opticalsystem longer, which in turn increases the size of the apparatus. Whenthe value is not more than the lower limit in the formula (9), the backfocal length is reduced, and the optical system cannot be provided.

The formulas (1) to (9) may be applied not only to the configurations inFIGS. 33 to 35, but also to any of the configurations of otherembodiments.

EXAMPLE 1

Example 1 is directed to the wide-angle imaging apparatus in FIG. 33. InExample 1, the focal length fa (mm), brightness Fno, and imaging range(half angle of view) ω (°) of the first optical system are as follows:fa=1.00, Fno=1.94, and ω=30 to 90°.

Table 1 shows numerical values of the first optical system in Example 1,where nd and νd indicate a refractive index and an Abbe number on the dline, respectively. The same is true in the following tables.

TABLE 1 No. rai dai nd νd a1  12.687 −3.68 Reflection surface a2  24.5823.68 Reflection surface a10 ∞ 0.15 Lens stop plane a11 −1.292 1.101.84666 23.8 Cemented lens a12  1.867 1.69 1.72916 54.7 a13 −3.223 0.11a14  5.759 1.62 1.72916 54.7 a15 −6.777 0.11 a16  3.970 1.62 1.5240456.4 a17 −11.959  0.37 a18 ∞ 2.0 1.51680 64.2 a19 ∞

In Example 1, the focal length fb (mm), brightness Fno, and imagingrange (half angle of view) ω (°) of the second optical system are asfollows:fb=0.75, Fno=1.94, and ω=0 to 30°.

Table 2 shows numerical values of the second optical system in Example1.

TABLE 2 No. rbi dbi nd νd b1  22.051 0.44 1.84666 23.8 b2  1.522 1.76b3  3.826 1.10 1.51680 64.2 b4  −5.316 3.68 b10 ∞ 0.15 Lens stop planeb11 −1.292 1.10 1.84666 23.8 Cemented lens b12 1.867 1.69 1.72916 54.7b13 −3.223 0.11 b14 5.759 1.62 1.72916 54.7 b15 −6.777 0.11 b16 3.9701.62 1.52404 56.4 b17 −11.959 0.37 b18 ∞ 2.0 1.51680 64.2 b19 ∞

In this embodiment, the first optical system and the second opticalsystem share the image-forming optical system. Therefore, the values ofa10 to a19 in Table 1 are equal to those of b10 to b19 in Table 2. Thesame is true in Examples 2.

The aspherical coefficients and conical coefficients in Example 1 areshown in the following. As described above, the first optical system andthe second optical system share the image-forming optical system.Therefore, the values of the a16 surface and the a17 surface are equalto those of the b16 surface and the b17 surface, respectively. The sameis true in Examples 2.A4=2.8000×10⁻⁵ , K=0.577  a1 surfaceA4=−3.000×10⁻⁶ , K=−0.478  a2 surfaceA4=−1.304×10⁻³A6=−3.388×10⁻³A8=4.371×10⁻⁴A10=−7.611×10⁻⁵K=−0.814  a16 surfaceA4=−1.214×10⁻²A6=6.983×10⁻⁴A8=−2.812×10⁻⁴A10=1.681×10⁻⁵K=7.287  a17 surface

The values of the formulas (2) to (9) in Example 1 are shown in thefollowing.fa=1fb=0.75f2≧d(f2=12.3, d=3.68)|f12/fa|=34.4r2=24.6r1/r2=0.52|fb−fa|/|fa|=0.25bf/fi=1.59

FIGS. 36A to 36C and FIGS. 37A to 37C show aberration curves of thefirst optical system and the second optical system in Example 1,respectively. FIGS. 36A and 37A show spherical aberration (mm), in whichthe solid line indicates values at a wavelength of 587.62 nm, the brokenline with a smaller pitch indicates values at a wavelength of 435.84 nm,and the broken line with a larger pitch indicates values at a wavelengthof 656.27 nm. The same is true in FIGS. 38A and 39A.

FIGS. 36B and 37B show astigmatism (mm), in which the solid lineindicates sagittal curvature of field, and the broken line indicatesmeridional curvature of field. The same is true in FIGS. 38B and 39B.FIGS. 36C and 37C show distortion (%). The same is true in FIGS. 38C and39C.

EXAMPLE 2

Example 2 is directed to the wide-angle imaging apparatus in FIG. 35. InExample 2, the focal length fa (mm), brightness Fno, and imaging range(half angle of view) ω (°) of the first optical system are as follows:fa=1.00, Fno=2.00, and ω=25 to 90°.

Table 3 shows numerical values of the first optical system in Example 2.

TABLE 3 No. rai dai nd νd a1  12.659 −13.82 Reflection surface a2 28.527 13.82 Reflection surface a10 ∞ 0.38 Lens stop plane a11 −2.6622.87 1.84665 23.8 Cemented lens a12 3.760 1.52 1.72916 54.7 a13 −4.1250.08 a14 5.822 0.94 1.72916 54.7 a15 737.670 0.08 a16 3.017 1.13 1.7291654.7 a17 6.441 0.38 a18 ∞ 2.00 1.51680 64.2 a19 ∞

In Example 2, the focal length fb (mm), brightness Fno, and imagingrange (half angle of view) ω (°) of the second optical system are asfollows:fb=0.80, Fno=2.00, and ω=0 to 25°.

Table 4 shows numerical values of the second optical system in Example2.

TABLE 4 No. rbi dbi nd νd b1  −2.519 0.60 1.67270 32.2 b2  −17.248 0.75b3  25.568 0.60 1.72825 28.3 b4  2.451 0.45 b5  16.328 1.13 1.51680 64.2b6  −10.878 5.10 b7  9.947 3.02 1.56883 56.0 b8  −8.364 1.13 b9  13.82b10 ∞ 0.38 Lens stop plane b11 −2.662 2.87 1.84665 23.8 Cemented lensb12 3.760 1.52 1.72916 54.7 b13 −4.125 0.08 b14 5.822 0.94 1.72916 54.7b15 737.670 0.08 b16 3.017 1.13 1.72916 54.7 b17 6.441 0.38 b18 ∞ 2.001.51680 64.2 b19 ∞

The aspherical coefficients and conical coefficients in Example 2 areshown in the following.A4=1.900×10⁻⁵A6=1.037×10⁻⁷ , K=0.271  a1 surfaceA4=−2.000×10⁻⁶A6=−4.713×10⁻⁹ , K=−0.515  a2 surface

The values of the formulas (2) to (9) in Example 2 are shown in thefollowing.fa=1fb=0.80f2≧d(f2=14.3, d=13.8)|f12/fa|=15.3r2=28.5r1/r2=0.44|fb−fa|/|fa|=0.20bf/f1=1.34

FIGS. 38A to 38C and FIGS. 39A to 39C show aberration curves of thefirst optical system and the second optical system in Example 2,respectively.

Embodiment 19

FIG. 40 shows the combination of a first reflection surface and a secondreflection surface and corresponds to a cross-sectional view taken alonga plane containing a central axis 9. FIG. 40 only illustrates lenses ofthe image-forming optical system and first reflection surfaces 221 thatare formed integrally with the lenses, and lenses of the refractiveoptical system and second reflection surfaces 221 that are formedintegrally with the lenses, but does not illustrate a third reflectionsurface, an imaging device, or the like.

In this configuration, the first reflection surfaces 221 have a convexsurface as seen from incident light from the object side, and the secondreflection surfaces 222 have a concave surface as seen from the incidentlight. In FIG. 40, two pairs of reflection surfaces are arranged fromside to side. However, half of the pairs can be applied to any of theconfigurations as shown in FIGS. 1 to 12.

Embodiment 20

FIG. 41 is a perspective view showing a wide-angle imaging apparatus inEmbodiment 20. Like Embodiments 5 to 10, this embodiment uses twowide-angle imaging optical systems. As shown in FIG. 41, a firstreflection surface 251 and a second reflection surface 252 are includedin a first wide-angle imaging optical system 257, while a firstreflection surface 254 and a second reflection surface 255 are includedin a second wide-angle imaging optical system 258.

In this embodiment, a central axis 253 of the first wide-angle imagingoptical system 257 and a central axis 256 of the second wide-angleimaging optical system 258 cross at an angle θ other than 180 degrees.That is, the central axis differs depending on the wide-angle imagingoptical system. On the other hand, each of the above embodiments showsan example of θ=180 degrees, which means that the central axis is commonto the wide-angle imaging optical systems.

In FIG. 41, the two central axes have an intersection point. However, itis also possible not to provide any intersection point between thecentral axes. In Embodiments 5 to 10, the central axes either may crossat a predetermined angle θ or may have no intersection point.

Embodiment 21

FIG. 42 shows a light transmission curve of Si₂AsTe₂, which is Si—As—Teglass. As can be seen from the graph, Si₂AsTe₂ has a highertransmittance in an infrared wavelength region (1 to 10 μm). Similarly,a material such as germanium also has a higher transmittance in theinfrared wavelength region. On the other hand, a reflecting mirrorformed, e.g., of a glass substrate coated with Al and MgF₂ can reflectat least 85% of light in a wide range of wavelength regions from visibleto infrared.

Accordingly, when the reflection surfaces formed, e.g., of a glasssubstrate coated with Al and MgF₂ are combined with the refractiveoptical system and the image-forming optical system that include lensesmade, e.g., of Si₂AsTe₂ or germanium in each of the above embodiments,the reflection surfaces reflect light, and both of the refractiveoptical system and the image-forming optical system transmit light in awide range of wavelength regions from visible to infrared. Thus, theapparatus can be used in a wide range of wavelength regions from visibleto infrared.

Embodiment 22

FIG. 43 shows an embodiment of a surveillance imaging system thatincludes any of the wide-angle imaging apparatuses in the aboveembodiments. A surveillance imaging apparatus 271 is installed in amonitoring space 275 and connected to a monitor 272 and an imageprocessor 273 by a cable 274. The images produced are processed by theimage processor 273 to create a panoramic image, which makes it possibleto perform real-time surveillance covering a wide range. The imageprocessor 273 also functions as a recording medium, so that the imagescan be stored and used as a database.

Moreover, when the combination of reflection surfaces and lenses asdescribed in Embodiment 13 is employed, the apparatus can be used in awide range of wavelength regions from visible to infrared. Thus,surveillance covering a wide range can be performed at any time of dayor night, and its condition can be recorded.

Embodiment 23

FIG. 44 shows an embodiment of a vehicle-mounted imaging system thatincludes any of the wide-angle imaging apparatuses in the aboveembodiments. When a vehicle-mounted imaging apparatus 281 is mounted,e.g., on the front, rear, or side view mirror portion of a vehicle 282,the panoramic image produced is displayed on a vehicle-installed monitor283, which is installed in the vehicle 282, so that the vehicle-mountedimaging apparatus 281 can serve as a rear view monitor, a front viewmonitor, or a side view monitor. This makes it possible for a driver tograsp the traffic situation in real time, thus ensuring more safety andcomfortable driving.

Embodiment 24

FIG. 45 shows an embodiment of a projection system that includes any ofthe wide-angle imaging apparatuses in the above embodiments. In thisprojection system, a spatial light modulator 292 is, e.g., a liquidcrystal panel that forms an optical image. A screen 294 is used as afocusing plane onto which an image is projected by a wide-angle imagingoptical system 291.

An image is formed on the spatial light modulator 292 that isilluminated by a light source 293, and then is magnified and projectedby the wide-angle imaging optical system 291 onto the screen 294. Thus,it is possible to achieve a video projector that provides an extremelywide field of view for an observer 295.

Embodiment 25

A wide-angle imaging apparatus of Embodiment 25 can be mounted on anobject, and the mounting angle can be adjusted. FIGS. 46 and 47 eachshow an embodiment when the wide-angle imaging apparatus is used as avehicle-mounted imaging apparatus. In these examples, a vehicle-mountedimaging apparatus 371 is mounted on the side face in the rear of avehicle 373. The basic configuration of the vehicle-mounted imagingapparatus 371 can be that of any of the wide-angle imaging apparatusesin the above embodiments.

In the example of FIG. 46, the vehicle-mounted imaging apparatus 371 ismounted on the vehicle 373 with its central axis substantiallyperpendicular to the ground that is to be imaged. In the example of FIG.47, a vehicle-mounted imaging apparatus 381 is mounted by changing themounting angle so that the central axis tilts with respect to theground. Such a change in mounting angle of the vehicle-mounted imagingapparatus with respect to the vehicle 373 allows the imaging range to bechanged from an imaging range 372 (FIG. 46) to an imaging range 382(FIG. 47).

When a movable means for changing the mounting angle of thevehicle-mounted imaging apparatus is provided so as to control themounting angle from the inside of the vehicle 373, the imaging rangeeasily can be changed, and thus the surrounding situation can bedetected and recognized precisely.

In this embodiment, the wide-angle imaging apparatus is used as avehicle-mounted imaging apparatus. However, it is not limited thereto,but also can be used, e.g., as a surveillance imaging apparatus.

Embodiment 26

FIGS. 48 to 50 each show an embodiment of a vehicle-mounted imagingapparatus. In FIG. 48, a vehicle-mounted imaging apparatus 391 ismounted on a vehicle 393. The diagonally shaded area 392 indicates animaging range. The vehicle-mounted imaging apparatus 391 includes amoving object sensing function, and the basic configuration of theapparatus itself can be that of any of the wide-angle imagingapparatuses in the above embodiments.

FIGS. 49 and 50 show wide-area images of the vehicle-mounted imagingapparatus 391. When a vehicle 394 comes into the imaging range 392 ofthe vehicle-mounted imaging apparatus 391, the moving object sensingfunction operates so that the image of the vehicle 394 appears on awide-area image 401 as a moving object image 402, as shown in FIG. 49.

Moreover, when the vehicle 394 moves, it is tracked automatically, andthe image of the vehicle 394 appears on a wide-area image 411 as amoving object image 412, as shown in FIG. 50. The moving object sensingfunction allows any moving object in the surroundings to be extractedand displayed, thus drawing more of the observer's attention.

The combination of Embodiments 17, 25, and 26 also can provide highlyimproved imaging as a wide-angle imaging system that includes a zoomfunction, an imaging range variable function with inclination, and amoving object sensing function.

INDUSTRIAL APPLICABILITY

As described above, the present invention includes the reflectiveoptical system with the first reflection surface and the secondreflection surface, the open portion provided between the firstreflection surface and the second reflection surface, thelight-transmitting portion provided in the second reflection surface,and the aperture provided in the first reflection surface, therebyproducing a panoramic image that covers a wide range, i.e., a maximumhorizontal angle of view of 360 degrees and a vertical angle of view ofabout 180 degrees. Moreover, the main optical system can be composed ofreflection surfaces that cause no chromatic aberration. This reduces notonly man-hours for design but also constrains on fabrication, so that asmall, lightweight, low-cost, and bright wide-angle imaging opticalsystem can be achieved. Therefore, the wide-angle imaging optical systemof the present invention is useful for a surveillance imaging apparatus,a vehicle-mounted imaging apparatus, and a projection apparatus.

1. A wide-angle imaging optical system comprising: a refractive opticalsystem having one or more lenses; a reflective optical system; and animage-forming optical system, wherein the reflective optical system andthe image-forming optical system are arranged in the indicated order asseen from a longer conjugate distance side and constitute a firstoptical system, and the refractive optical system and the image-formingoptical system are arranged in the indicated order as seen from thelonger conjugate distance side and constitute a second optical system,wherein the reflective optical system comprises a first reflectionsurface that directly reflects rays of light from an object, and asecond reflection surface that reflects rays of light from the firstreflection surface, wherein the refractive optical system comprises atleast one lens located on an object side of the second reflectionsurface, wherein an open portion is provided between the firstreflection surface and the second reflection surface, and rays of lightfrom the object enter the open portion, wherein a light-transmittingportion is provided in the second reflection surface and transmits raysof light that have entered the refractive optical system, and wherein anaperture is provided in the first reflection surface and allows rays oflight from the second reflection surface and rays of light that haveentered the light-transmitting portion from the refractive opticalsystem to enter the image-forming optical system, and wherein nointermediate image is formed inside the wide-angle imaging opticalsystem.
 2. The wide-angle imaging optical system according to claim 1,wherein the first optical system and the second optical system share theimage-forming optical system.
 3. The wide-angle imaging optical systemaccording to claim 1, satisfying the relationship expressed byfa>0fb>0 where fa is a combined focal length of the first optical system,and fb is a combined focal length of the second optical system.
 4. Thewide-angle imaging optical system according to claim 1, satisfying therelationship expressed byf2≧d where f2 is a focal length of the second reflection surface, and dis a distance on an axis between the first reflection surface and thesecond reflection surface.
 5. The wide-angle imaging optical systemaccording to claim 1, satisfying the relationship expressed by|f12/fa|>5 where fa is a combined focal length of the first opticalsystem, and f12is a combined focal length of the first reflectionsurface and the second reflection surface.
 6. The wide-angle imagingoptical system according to claim 1, satisfying the relationshipexpressed byr2>00.3<r1/r2<0.7 where r1 is a radius of curvature of the first reflectionsurface, and r2 is a radius of curvature of the second reflectionsurface.
 7. The wide-angle imaging optical system according to claim 1,wherein the refractive optical system comprises a first lens group withnegative power and a second lens group with positive power that arearranged in the indicated order as seen from the object side.
 8. Thewide-angle imaging optical system according to claim 1, wherein at leastone of the first reflection surface and the second reflection surface isa rotationally symmetrical aspheric surface in shape.
 9. The wide-angleimaging optical system according to claim 1, wherein a magnification forimage formation of the first optical system and a magnification forimage formation of the second optical system have the same sign.
 10. Thewide-angle imaging optical system according to claim 1, wherein amagnification for image formation of the first optical system and amagnification for image formation of the second optical system are bothnegative.
 11. The wide-angle imaging optical system according to claim1, wherein at least one focal point of the first reflection surfacecoincides with at least one focal point of the second reflectionsurface.
 12. The wide-angle imaging optical system according to claim 1,wherein a lens stop is located inside the image-forming optical systemor between the image-forming optical system and the second reflectionsurface.
 13. The wide-angle imaging optical system according to claim12, wherein a focal point of the second reflection surface coincide witha center of the lens stop.
 14. The wide-angle imaging optical systemaccording to claim 1, wherein a shielding member is formed near theperiphery of the aperture.
 15. The wide-angle imaging optical systemaccording to claim 14, wherein the shielding member supports theimage-forming optical system.
 16. The wide-angle imaging optical systemaccording to claim 1, wherein the image-forming optical system comprisesa hood that limits rays of light entering the image-forming opticalsystem.
 17. The wide-angle imaging optical system according to claim 1,wherein lenses of the image-forming optical system are arranged in thefollowing order as seen from the object side: a negative lens, apositive lens, and a positive lens.
 18. The wide-angle imaging opticalsystem according to claim 1, wherein lenses of the image-forming opticalsystem are arranged in the following order as seen from the object side:a negative lens, a positive lens, a positive lens, and a positive lens.19. The wide-angle imaging optical system according to claim 1, whereinthe refractive optical system comprises a hood that limits rays of lightentering the refractive optical system.
 20. The wide-angle imagingoptical system according to claim 1, wherein the first reflectionsurface is formed integrally with a lens of the image-forming opticalsystem.
 21. The wide-angle imaging optical system according to claim 20,wherein a shape of the first reflection surface is substantially thesame as a shape of a portion of the lens of the image-forming opticalsystem that corresponds to the aperture.
 22. The side-angle imagingoptical system according to claim 20, wherein a shape of the firstreflection surface differs from a shape of a portion of the lens of theimage-forming optical system that corresponds to the aperture.
 23. Thewide-angle imaging optical system according to claim 1, wherein thesecond reflection surface is formed integrally with a lens of therefractive optical system.
 24. The wide-angle imaging optical systemaccording to claim 23, wherein a shape of the second reflection surfaceis substantially the same as a shape of a portion of the lens of therefractive optical system that corresponds to the light-transmittingportion.
 25. The wide-angle imaging optical system according to claim23, wherein a shape of the second reflection surface differs from ashape of a portion of the lens of the refractive optical system thatcorresponds to the light-transmitting portion.
 26. The wide-angleimaging optical system according to claim 1, wherein the image-formingoptical system comprises a third reflection surface that reflects raysof light imaged.
 27. The wide-angle imaging optical system according toclaim 1, wherein the refractive optical system and the image-formingoptical system are transparent to an infrared wavelength regionincluding 1 to 10 μm.
 28. A wide-angle imaging apparatus comprising: thewide-angle imaging optical system according to claim 1; and an imagingdevice for picking up an image formed by the image-forming opticalsystem.
 29. The wide-angle imaging apparatus according to claim 28,wherein a plurality of wide-angle imaging optical systems and theimaging devices that correspond to each of the plurality of wide-angleimaging optical systems are arranged so as to produce separate images ofan object.
 30. The wide-angle imaging apparatus according to claim 29,wherein two wide-angle imaging optical systems and the imaging devicesthat correspond to each of the two wide-angle imaging optical systemsare arranged so as to produce separate images of an object, and when anaxis that joins centers of curvature of the first reflection surface andthe second reflection surface is identified as a central axis, the twowide-angle imaging optical systems are arranged symmetrically withrespect to an axis perpendicular to the central axis.
 31. The wide-angleimaging apparatus according to claim 29, wherein the plurality ofwide-angle imaging optical systems share a single imaging device. 32.The wide-angle imaging apparatus according to claim 28, wherein when anarea in which rays of light enter the reflective optical system isidentified as a first imaging area, and an area in which rays of lightenter the refractive optical system is identified as a second imagingarea, an image picked up by the imaging device includes a circular imagethat is obtained by taking the second imaging area and an annular imagethat is obtained by taking the first imaging area and formed outside thecircular image, the first imaging area and the second imaging area donot overlap with each other, and the circular image and the annularimage are arranged continuously.
 33. The wide-angle imaging apparatusaccording to claim 28, wherein a protective member is arranged so as tosurround the open portion.
 34. The wide-angle imaging apparatusaccording to claim 33, wherein the protective member is provided with afilm for preventing internal reflection.
 35. The wide-angle imagingapparatus according to claim 33, wherein the protective member is in theform of a substantially frustoconical, and an inner diameter of theprotective member at the first reflection surface differs from an innerdiameter of the protective member at the second reflection surface. 36.The wide-angle imaging apparatus according to claim 28, wherein at leastone of the refractive optical system and the image-forming opticalsystem has a zoom function.
 37. The wide-angle imaging apparatusaccording to claim 28, wherein the wide-angle imaging apparatus can bemounted on an object, and a mounting angle can be adjusted.
 38. Thewide-angle imaging apparatus according to claim 28, comprising a movingobject sensing function.
 39. A surveillance imaging apparatus comprisingthe wide-angle imaging optical system according to claim
 1. 40. Avehicle-mounted imaging apparatus comprising the wide-angle imagingoptical system according to claim
 1. 41. A projection apparatuscomprising the wide-angle imaging optical system according to claim 1.42. A wide-angle imaging optical system comprising: a refractive opticalsystem; a reflective optical system; and an image-forming opticalsystem, wherein the reflective optical system and the image-formingoptical system are arranged in the indicated order as seen from a longerconjugate distance side and constitute a first optical system, and therefractive optical system and the image-forming optical system arearranged in the indicated order as seen from the longer conjugatedistance side and constitute a second optical system, wherein thereflective optical system comprises a first reflection surface thatdirectly reflects rays of light from an object, and a second reflectionsurface that reflects rays of light from the first reflection surface,wherein an open portion is provided between the first reflection surfaceand the second reflection surface, and rays of light from the objectenter the open portion, wherein a light-transmitting portion is providedin the second reflection surface and transmits rays of light that haveentered the refractive optical system, wherein an aperture is providedin the first reflection surface and allows rays of light from the secondreflection surface and the refractive optical system to enter theimage-forming optical system, and wherein the wide-angle imaging opticalsystem satisfies the relationship expressed by|fb−fa|/|fa|<0.5 where fa is a combined focal length of the firstoptical system, and fb is a combined focal length of the second opticalsystem.
 43. A wide-angle imaging optical system comprising: a refractiveoptical system; a reflective optical system; and an image-formingoptical system, wherein the reflective optical system and theimage-forming optical system are arranged in the indicated order as seenfrom a longer conjugate distance side and constitute a first opticalsystem, and the refractive optical system and the image-forming opticalsystem are arranged in the indicated order as seen from the longerconjugate distance side and constitute a second optical system, whereinthe reflective optical system comprises a first reflection surface thatdirectly reflects rays of light from an object, and a second reflectionsurface that reflects rays of light from the first reflection surface,wherein an open portion is provided between the first reflection surfaceand the second reflection surface, and rays of light from the objectenter the open portion, wherein a light-transmitting portion is providedin the second reflection surface and transmits rays of light that haveentered the refractive optical system, wherein an aperture is providedin the first reflection surface and allows rays of light from the secondreflection surface and the refractive optical system to enter theimage-forming optical system, and wherein the wide-angle imaging opticalsystem satisfies the relationship expressed by1.2<bf/fi<1.8 where bf is a back focal length of the image-formingoptical system measured in terms of air when rays of light from anobject at infinity enter the image-forming optical system in parallel,and fi is a combined focal length of the image-forming optical system.